Semi-conductor devices have recently become more highly integrated and smaller in size than ever before, which generated needs to develop sophisticated materials and processes for forming thin films in the fabrication of semi-conductor devices. In response to such needs, there have been developed, for example, barium strontium titanate(BST) used in a capacitor for dynamic random access memory(DRAM), and ferroelectric materials such as lead zirconate titanate(PZT), strontium bismuth titanate(SBT), bismuth lanthanum titanate(BLT) used in ferroelectric random access memory(FRAM) and yttrium stabilized zirconia(YSZ) and metal oxides such as TiO.sub.2 and ZrO.sub.2. Thin films of such materials are prepared by using such techniques as radio frequency magnetron sputtering, ion beam sputtering, reactive co-evaporation, metal organic decomposition(MOD), liquid source misted chemical decomposition(LSMCD), laser ablation and metal organic chemical vapor deposition(MOCVD).
Among these methods, MOCVD is carried out by vaporizing one or more organometallic precursor compounds, transporting, using a carrier gas, the vaporized precursor(s) to the surface of a heated solid substrate and forming a thin film on the surface of the substrate through a chemical reaction. The MOCVD method is advantageous in that: it can be carried out at a relatively low temperature; the constitution and deposition rate of the thin film can be readily controlled by changing the amounts of the source materials and the carrier gas; and the final thin film has good uniformity and excellent conformal step coverage without causing any damage on the surface of the substrate. Therefore, MOCVD is widely used in manufacturing semi-conductor devices such as DRAM and FRAM.
Generally, a precursor for CVD is required to have such properties as a high vapor pressure, high purity, high deposition rate, easy handling, nontoxicity, low cost and a suitable deposition temperature. However, conventional organometallic compounds for CVD such as metal alkyls, metal alkoxides and .beta.-diketonates have many drawbacks. For example, metal alkyls having relatively high vapor pressures such as Pb(C.sub.2 H.sub.5).sub.4 are very toxic (see Reference of Organometallic Dictionary). Metal alkoxides are sensitive to moisture, which relatively expensive metal .beta.-diketonates have low vapor pressures and are solids at room temperature, posing handling difficulties in CVD process(see Anthony C. Jones et al., Journal of the European Ceramic Society, 19(1999), 1431-1434).
Besides the above problems, Ti(O.sup.i Pr).sub.4 (titanium tetraisopropoxide) is unstable at room temperature and a thin layer obtained from Ti(O.sup.i Pr).sub.2 (tmhd).sub.2 (tmhd=tetramethylheptanedionate) has a fluctuating amount of Ti depending on the substrate temperature(see Jung-Hyun Lee et al., Electrochemical and Solid-State Letters, 2(10) (1999), 507-509).